1. Field of the Invention
This invention relates to improvements in an intake system for an internal combustion engine equipped with a supercharger, and more particularly to an air bypass device for bypassing or releasing intake air from the downstream side to the upstream side of the supercharger.
2. Description of the Prior Art
Automotive internal combustion engines equipped with a supercharger are usually provided with an air bypass device to bypass or recirculate intake air from the upstream side to the downstream side of the compressor of a supercharger. An example of such an air bypass device is disclosed in Japanese Utility Model Publication No. 63-46628 and shown in FIG. 1 of the drawings of the present application. In FIG. 1, the air bypass device includes an air bypass passage 2 through which intake air in the downstream side of a turbocharger 1 is bypassed to the upstream side of the turbocharger 1 in an initial period of deceleration of the engine. A recirculation or bypass valve 3 is disposed in the bypass passage 2 and adapted to be opened by the pressure differential between a first pressure chamber 6 in communication with the upstream side of a throttle valve 5 and a second pressure chamber 7 in communication with the downstream side of the throttle valve 5. The bypass valve 3 is connected to and movable with a diaphragm which defines the first and second pressure chambers 6, 7 on the opposite sides thereof. Upon opening of the bypass valve 3, the pressure prevailing in the downstream side of the turbocharger compressor is prevented from an excessive rise due to closure of the throttle valve at a sudden deceleration of the engine.
The above discussed conventional air bypass device as shown in FIG. 1 is for the internal combustion engine which is provided with only one air intake passageway which is communicable with all of the engine cylinders. However, difficulties have been encountered in the case where such a conventional air bypass device is applied to a V-type internal combustion engine in which two independent air intake passageways are provided respectively for the left and right side banks of the engine. In such an engine, an upstream side air intake passageway is branched into the two downstream air intake passageways at a position downstream of the turbocharger, in which two throttle valves are respectively disposed in the downstream air intake passageways. In this arrangement, the air bypass device includes an air bypass passage through which intake air is recirculated back from the downstream side to the upstream side of the turbocharger. The air bypass passage is provided with an air bypass valve for controlling air flow in the air bypass passage.
The encountered difficulties will be discussed: If the air bypass valve is disposed one-sided to one of the two downstream air intake passageways, distribution of intake air to the two air intake air passageways becomes unequal under the action of bypass air flow in the upstream side of the throttle valves during a transition period from a sudden deceleration to a re-acceleration. This phenomena is common in low and medium engine speed ranges.
In order to improve such unequal distribution of intake air, it may be considered to dispose the air inlet of the air bypass passage at an upstream position far from an air intake passageway branched section from which the air intake air passageway is branched off. However, this unavoidably prolongs the distance of the air inlet from the throttle valves, and therefore intake air cannot be smoothly inducted into engine cylinders during the transition period from the sudden deceleration situation to the re-acceleration situation, thereby deteriorating response in acceleration and deceleration. Additionally, in a usual arrangement in which control of the air bypass valve is made in accordance with intake vacuum prevailing in the downstream side of the throttle valves, the length of a vacuum line through which intake vacuum for controlling the air bypass valve is supplied is enlarged, thereby degrading the controllability of the air bypass valve.
Furthermore, it may be considered that each of the two air intake passageways is provided with the air inlet of the air bypass passage and the air bypass valve. However, this unavoidably increases the number of parts required, such as pipings, and thereby increases production costs and degrades assembly operation.